The present invention relates in general to fluid mixing controls, and in particular to a new and useful device for mixing hot and cold fluid together in a computer regulated manner so as to produce a mixture having a selected temperature with a high degree of accuracy and with a short response time.
Arrangements are known for mixing hot and cold water together to produce mixed water having a selected temperature. U.S. Pat. No. 4,359,186 to Kiendel discloses a mixing valve arrangement which utilizes motor driven valves to supply hot and cold water to a mixing chamber of a water faucet. Temperature of the water in the mixing chamber is detected and used, along with the flow of fluid through the mixing chamber, as a control signal in an analog circuit for controlling the motors.
The Kiendel patent does not disclose the usefulness of a microcomputer which can be programmed to a selected temperature setpoint.
Additional U.S. patents which are relevant to the present invention include U.S. Pat. No. 4,429,422 to Wareham; U.S. Pat. No. 4,277,832 to Wong; and U.S. Pat. No. 4,189,792 to Veach.
Wareham uses an open loop system which does not utilize a temperature signal fed back from the faucet outlet. Wong utilizes a microprocessor for controlling the flow of fuel to a fuel nozzle. Veach, while controlling the flow of hot and cold water to a faucet, does not use closed loop feedback control. U.S. Pat. No. 4,383,551 to Lynch et al also discloses a liquid mixing device where valves are electronically controlled. This device uses pulsed jets of hot and cold water which are regulated by solenoid valves. It takes approximately twenty seconds for the device to change temperatures from 100 to 65 deg F. and several additional measures are necessary to dampen the violent impulses caused by pulsing liquids.